A popular device for handling large amounts of information in a data processing system is the data storage library. These libraries store and manage large numbers of data cartridges, typically containing magnetic tape on which data is recorded. A data storage library is composed of arrays of storage cells, each cell being formed to contain a single data cartridge. The arrays each hold a plurality of data cartridges, and each data cartridge has some kind of identifying information, such as a label or bar code. Typically, the arrays surround a robotic arm which has an optical system for selecting cartridges, and is operable to locate a particular storage cell and retrieve and transport a data cartridge therefrom. The cartridges must be positioned within the storage cells in a precise manner if the robotic arm is to grasp them correctly.
Different hardware manufacturers have independently developed data cartridges that are unique to each manufacturer. Accordingly, the owner of a data storage library may wish to use a variety of different cartridge types within a single library system. However, it has traditionally been a problem in library design to accommodate data cartridges of different sizes into the same library enclosure. One approach is to provide a fixed number of storage cells sized for each different type of cartridge within the data storage library. However, this solution is undesirable since each library must be specially customized with fixed numbers of storage cells corresponding to the owner's needs, and those needs may change over time.
If a single size storage cell is used for storing data cartridges of different sizes, the storage cell width and length must be sufficient to allow the widest and longest cartridge to easily be contained therein. However, for data cartridges with substantially smaller dimensions than the storage cell size, misalignment of the cartridges within the storage cells often occur and result in transfer difficulties for the robotic arm. In particular, cartridges having different widths will not be positioned in a standard location within the storage cells. This width variation has typically been addressed by attempting to center the cartridges within the storage cells, however, the centering attempts often leave cartridge labels in skewed positions which the optical system of the robotic arm must resolve with its depth of field capability. The skewed alignment of the cartridges also reduces the reliability of engagement by the robotic arm. Furthermore, cartridges having different lengths will extend forwardly, if at all, from the storage cells at different distances, further reducing the reliability with which the robotic arm can accomplish cartridge transfer.